1. Field of the Invention
The present invention relates to an infrared ray detection device, a method of fabricating the same and an infrared ray camera which have structure for supporting a detection cell by a supporting part.
2. Related Art
A non-cooling (thermal) type infrared ray sensor is a device which absorbs a focused infrared ray by an infrared ray detector to convert radiation energy of the infrared ray into electric signals. The sensor has a characteristic in which detection cells made of an infrared ray-absorption material and a thermoelectric conversion device are thermally separated from outside. In order to realize such a structure, a technique of surface micromachining or bulk micromachining is necessary. The non-cooling (or uncooled) type infrared ray sensor has an advantage in which it is possible to reduce production cost and size, compared with a cooling infrared ray sensor which requires an expensive and large cooler.
In order to perform thermal separation, it is important to install the detection cell under vacuum and to lower thermal conductance of a supporting structure for physically and electrically connecting the detection cells to a substrate. The thermal conductance of the supporting structure becomes smaller as the supporting structure is finer. Therefore, in order to improve sensitivity of the sensor, it is necessary to reduce design rule of semiconductor process for forming the above structure (see JP-A 2002-107224 (Kokai)).
In the above document, the cross sectional structure of a supporting leg for supporting the detection cells has a wiring part and an insulating part for protecting the wiring part. If the wiring part is formed in shape shifted in left or right direction from the center of the insulating part, the supporting leg is distorted in a substrate-surface direction, thereby causing physical contact. The shift of the wiring part occurs due to mask matching displacement of photolithography in the process for forming the supporting leg. The width of the supporting leg is 1 μm or less. Even when the wiring part is shifted 0.1 μm, a large distortion occurs. Therefore, matching accuracy has to be restrained within 0.1 μm or less.
Sensitivity of the non-cooling infrared ray sensor is inversely proportional to thermal conductance of the supporting leg. If the supporting leg contacts some part on a thermal transmission path, thermal insulation performance of the detection cell deteriorates significantly. Such a structural problem occurs due to external cause such as mechanical shock or dripping as well as structural stress by the structure itself.
The stress includes a thermal stress caused by a difference between a processing temperature at a time of forming the structure and a device operational temperature and an internal stress caused by a material forming of the structure. If the structure is spatially symmetric, these stresses are canceled inside of the structure. However, if the structure is asymmetry, the structure is deformed in an asymmetric direction.
In order to avoid requirement of such a strict matching accuracy, a robust supporting leg structure capable of reducing the distortion due to the internal stress is necessary.